Maize Lowers the N2O Emissions from Maize/soybean Intercropping

Interspecific interactions between intercropped maize and soybean are expected to cycle soil nitrogen efficiently and avoid N2O emissions. However, the unique interactions of maize and soybean with nitrogen cycling bacteria makes it hard to predict the crop-specific impact on soil N2O production. We conducted a field microcosm experiment with root separation to simulate monoculture and intercropping with maize and soybean. Intercropped maize reduced the N2O emissions by 16–41%, compared to monoculture maize. This was related to reduced nitrification by ammonia-oxidizing bacteria and denitrification reactions (as indicated by the abundance of nirS and nirK gene copies), as well as drier soil conditions and lower soil NO3−-N levels. Soil N2O emissions were the same in monoculture and intercropped soybean, suggesting stable denitrification (based on nirS, nirK and nosZ genes) with constant soil physicochemical conditions. As monoculture maize can stimulate soil N2O emission through denitrification, this work justifies the adoption of maize-soybean intercropping as a low N2O-emitting practice in sustainable agriculture, due to its beneficial effects on soil biology and biochemistry.